Field of the Invention
The present invention relates to a transfer member for electrophotography having a low-adhesion surface layer which is used in an image forming apparatus of an electrophotographic system such as a copying machine and a printer.
Description of the Related Art
In recent years, an intermediate transfer system has been used in a color electrophotographic apparatus. In the intermediate transfer system, developed images in four colors of yellow, magenta, cyan and black are once successively transferred (primary transfer) from a photosensitive member to an intermediate transfer member, and then color images formed on the intermediate transfer member are collectively transferred (secondary transfer) to a transfer material such as paper. As the intermediate transfer member used here, for example, a semi-conductive belt containing carbon black dispersed in a polyimide resin is known.
However, in the image forming apparatus in which high image quality and high durability are required, such a semi-conductive belt itself may not be sufficient. High image quality as described here refers to the fact that a toner image is secondarily transferred at a high transfer rate from a belt to a transfer material (for example, paper). When the transfer rate is low, an omission may occur in the toner image transferred to the transfer material; density unevenness may occur in the image outputted in this state; and color unevenness may occur in the transfer of four-color images. Further, high durability refers to the state where a high transfer rate is maintained in the secondary transfer process, and density unevenness and color unevenness hardly occurs even in repeated image output.
Japanese Patent Application Laid-Open No. H09-138594 and Japanese Patent Application Laid-Open No. 2012-078801 each disclose, in order to achieve high image quality, an effective technique of imparting excellent secondary transferability by coating the surface of a transfer member with a low-adhesion material such as a fluororesin and a silicone resin to improve toner release properties.
Specifically, Japanese Patent Application Laid-Open No. H09-138594 discloses a technique of reducing adhesion of remaining toner or the like by incorporating a linear perfluoropolyether rubber into a surface layer.
Further, Japanese Patent Application Laid-Open No. 2012-078801 discloses a technique of forming a hard-coat layer by coating the surface of a transfer member with a graft type copolymer resin having a polymerizable fluororesin as a main chain and polysiloxane as a side chain and curing the coating film by a curing unit such as ultraviolet irradiation. In this technique, the polysiloxane side chain chemically bonded to the main chain provides excellent physical resistance such as damage resistance and wear resistance, and good secondary transferability derived from the main chain is imparted to the transfer member.
One aspect of the present invention is directed to providing a transfer member for electrophotography which has excellent secondary transferability to prevent occurrence of density unevenness and color unevenness in a printed image and has resistance to physical degradation in the transfer process of an electrophotographic system.
Another aspect of the present invention is directed to providing an electrophotographic image forming apparatus which can stably form a high quality electrophotographic image.